"For Christ also hath once suffered for sins, the just for the unjust, that he might bring us to God, being put to death in the flesh, but quickened by the Spirit..." (1 Peter 3:18)
Jesus suffered for the sins of the righteous and the unrighteous. He died for all of us - Christian, Jew, Muslim, Buddhist, Hindus, Atheists and everyone in between. His death paid for our sins. His resurrection opened the gates of Heaven and gave each one of us the opportunity to accept the gift offered...salvation.
The commentary written on this verse (and the two that follow) seems to differ. Each Christian denomination teaches something a bit different, but there are no supporting verses for it. What we do know, through our reading of God's Word, is that the salvation Jesus brought to us was preached in the Old Testament as well as the New. We know that Christ is the key to our salvation - without him, without acceptance of his sacrifice as the Son of God, we are not saved. We know we cannot get there by works alone and that just being a good, kind person does nothing but leave a nice epitaph on our tombstone. There must be belief, there must be faith and there must be acceptance!
Belonging to a religious denomination offers us a community of Christians to worship with, to pray with, to grow with - but it is not a replacement for the personal relationship one develops by reading the Word of God! Make a place for Jesus in your life, in your heart. Read your Bible, talk to God - he listens!